NAOJ GW Elog Logbook 3.2
The High voltage driver (first picture) is from Matsusada Precision (PZJ-0.15P-LVS2) and the datasheet can be found at the following link: https://www.matsusada.com/pdf/pzj.pdf
The piezo used for the SHG cavity (first measurement) is from Piezomechanik GmbH (HPCh 150/15-8/3) and has a capacity of 790nF.
The piezo used for the IR mode cleaner (second measurement) is from PI (P-025.20H PICA) and has a capacity of 430nF.
We measured two HVDs. One is HVD used for SHG, the other is a new SHG. Each trace data is taken with two different frequency spans and overlapped. This is to make measurement precise.
As you can see from below, the TF of HVD truly has feature like low-pass.
The High voltage driver (first picture) is from Matsusada Precision (PZJ-0.15P-LVS2) and the datasheet can be found at the following link: https://www.matsusada.com/pdf/pzj.pdf
The piezo used for the SHG cavity (first measurement) is from Piezomechanik GmbH (HPCh 150/15-8/3) and has a capacity of 790nF.
The piezo used for the IR mode cleaner (second measurement) is from PI (P-025.20H PICA) and has a capacity of 430nF.
From the experiment we had done, we had got an open loop transfer function of the SHG control loop. To optimize this control loop, we changed the parameters of the servo (corner frequency and gain) monitoring the open loop transfer function, its unity gain frequency, and phase margin, using the network analyzer (Agilent 36540A).
I show several pairs of parameters below. On the 7th column we have 224Hz unity gain freq. and 30 degree phase margin, it seems somewhat better than the others.
With a gain greater than 2000, system became unstable.
Still, there need to be more investigation.
| Corner freq.[Hz] | Gain[dB] | Unity gain freq.[Hz] | Phase margin[degree] |
| 10 | 1000 | 1000 | 1.5 |
| 10 | 200 | 512 | 11 |
| 10 | 100 | 352 | 14 |
| 10 | 50 | 224 | 23 |
| 3 | 1000 | 672 | 0.6 |
| 1 | 1000 | 384 | 15 |
| 0.3 | 1000 | 224 | 30 |
| 0.1 | 1000 | 96 | 42 |
| 0.03 | 1000 | 32 | 59 |
We used Agilent 35670A network analyzer.
All traces are pieced together from traces with different frequencies span.
Firstly, we investigated frequency response of an adder we used (1st figure).
We got a flat response in magnitude and phase.
Secondly, we took dark noise spectra of the adder and Agilent 35670A (2nd figure).
Thirdly, we measured a mechanical transfer function of SHG (3rd figure).
We guessed a peak around 25kHz indicated a resonance point of PZT.
Lastly, we measured an open loop transfer function of SHG (4th figure).
Unity gain frequency is around 1kHz.
| [urad] | |
| PR yaw | 0.78 |
| PR pitch | 1.40 |
| BS yaw | 2.21 |
| BS pitch | 4.31 |
The reference for the residual motion can be found in the previus entry n.428
The original resistor was 51 - 1W and the resistor now is 5k1 - 1/4W. The gain of that channel increased by a factor of 100 as expected.
Today, I made some measurements about the green light. The process is
Firstly, the green light was stable. Then I sent message to Matteo, and Matteo thought it's saturation. Actually this is what I and Tomura-san found last week. So I decided to use the filter to check it. And I found Matteo was right.
Secondly, the green light became unstable. I measure the noise spectrum at this moment. I want to see what will happen after a while.
Thirdly, after a while, the green light becomes stable again. I measure the noise spectrum again. This is different from the previous one certainly. Then I want to see what will happen after a while again.
Fourthly, after a long-while, the green light becomes unstable again. And I told it to Matteo, Matteo thought it could be cause by beat of two signals. So I checked it on the oscilloscope, it turns out that we can see slow variation of signal on oscilloscope(3rd picture). Indeed, it looks like a beat signal.
The main difference between unstable and stable signal is a peak around 2.7kHz. Matteo suggested to remove the thermal dissipator. After removing it, we measure noise spectrum again. It's almost the same with the stable spectrum we measured before.
Above all, we find that a reason of instability is the resonance of thermal dissipator. Actually, we can see from noise spectrum, the only difference is the peak around 2.7kHz. So there is also at least another reason of instability, it's caused by the peak around 650Hz. And we can see its harmonic peak. (But we cannot see this frequency fluctuation on oscilloscope clearly)
(Sorry for not using matlab to make plot. It's because of my saving of wrong format data.)
The first picture, it's the unstable noise spectrum.
The second picture, it's the stable noise spectrum.
The third picture, it's the long term signal in the view of oscilloscope(unstable).
The fourth picture, it's thermal dissipator.
The fifth picture, the same time scale with the 3rd picture of oscilloscope(stable). Actually, it just doesn't have something like beat or resonance. As you can see it's not stable for a long time.
I aligned for probe laser(1310 nm).
I changed the IU alignment and scanned.
I got the result like this figure.
In it, the measured peak AC signal value (~0.006 V) is lower than before(~0.02 V).
Also, secondary peak can't be seen well.
Next time, I have to align again in order to get a good result.
Pictures of the opened PR chamber.
3 mirrors have been added to obtain the IR and green references.
G1 is the green beam reflected by the dichroic
IR 1 is the IR beam after the Faraday Isolator and a folding mirror
GR2 and IR2 are reflected by the same mirror ( between the green folding mirror and the dichroic and between the 2 metallical structures).
They can be seen on the "PR references" picture.
I will try to upload a more precise optical scheme of this chamber
Using the simulations I compared the surface reference sample scan signal when changing some parameters.
First, I made the scan of the surface reference sample with the 633nm probe. The figure1 shows the signal AC/DC when I change the size of the detector.
Then I set 1mm of detector size and only change the wavelength and probe waist. Figure2
The interference a bit larger and the intensity is about half of the 633nm probe. This may be due to the different focusing alignment required for the 1310nm. However, it still doesn't explain the behavior of experimental data that have 2 large peaks instead of one.
Before moving anything we did the coil check again one by one, each of them has response to the noise and the amplitude of the motion is similar. Then we tried to adjust the picomotor in order to put the beam back at the reference we put outside the BS chamber, which is the transmission of BS mirror. Of course after moving the picomotor we should put the PSD signal back to zero, then when we tried to close the loop, we found even we put the offset as the value when the mirror is free, the correction signal is around 5 or 6(should be around zero). This means we cannot control the PR mirror anymore.
We tried to go on,by changing the local control offset, we were able to sent the beam to end and saw it on the CCD camera. Then as usual the next step should be align the reflection of the input mirror to the injection beam. But we cannot see the reflection as the nearest window of the bench, so we check the reflection beam on the 2 inch mirror to align it. Yaw of the reflection looks fine, so we only tried to adjust the pitch, the range we can move of the pitch is between -3.5 to 4. This is the normal range, but with this range we are not able to bring back the beam at the good position.The possible reason should be the beam was not well aligned, so with the PR picomotor and BS local control, we tried to align the beam better, at the same time looking at the beam at the end for not losing it. But then we reach the limit of BS local control, we are not far from well-aligned. Actually during our adjustment, the BS range was slightly get smaller, which is very strange.
V
In the attachment, it is the test we did to each magnet, when we sent a sine wave with amplitude 1V and frequency 1Hz, the motion of pitch and yaw.
The next step we are going to do :
1. check the open loop transfer function of two mirrors
2. try to bring back the beam on the BS mirror to the right height, which means we can receive the whole round beam with the two inch mirror we put at the back side of the BS mirror, and got the reflection of it outside the window.
Note to switch on alert light after turning on the laser.
Some tips from Yuefan
1.Remember to switch off the piezo driver of SHG, otherwise it will drift away from the right position. It's located in the right side of the third shelf counting from the bottom.
2.The Laser power we use is around 1.2W, the value can be adjusted by the left knob on the panel.
The procedure of using the control system(the computer is always on, the system is based on Labview)
1.The document is under Project Explorer, the name is Eleonora-e-Manuel.
2.Control and demonstration panel:
BS and PR: under SAS_NM2b, the name is: tele12_control.vi
IM: under SAS_NM1b, the name is: IM1_contol.vi
Em: under SAS_EM2a, the name is: EM_contol.vi
3.Measurement of transfer function:
PR and BS: under SAS_NM2b, the name is: advtransfer_functions_tele.vi
IM: under SAS_NM1b, the name is: transfer_functions.vi
EM: under SAS_EM2a, the name is: transfer_functions2.vi
4.The local control and mode-matching of each mirror:
After opening each document, we can see clearly the mirror we want to control. Just by clicking on the dark green button, we can close the control loop. There is a very important parameter, offset. By setting different value, we can get a different orientation of this mirror. By this way, we can adjust the mirror to the right place. The right place can be checked by confirming the reflecting reference laser is on the right remark. The remark is made by Yuefan. For example, there is a remark on the viewport of BS tank. If the reference laser is reflected to this point, it means that the PR is in the right position.
For BS, we need to adjust its position slowly. We can do it with the help of diaphragm. Because we have several diaphragms in TAMA's arm pipe(between IM and EM).
After adjusting BS, we should see some high order modes in the CCD. Then we need to align the optical layout. There are two kinds of higher order modes. By adjusting BS and PR, we can eliminate the Hermite-Gaussian mode. However, the Laguerre-Gaussian mode is caused by the waist mismatch. We can solve this by moving two lenses behind AOM.
5.Try to find the reason of BS high motion of microrad
(1)The power supply. We usually stabilized voltage supply for the laser. Because PR's control is good enough. We changed their power supply, and then we find nothing changed.
(2)The data acquisition system. By changing the connection port of BS, we find nothing changed. Because we use the same data acquisition for all the data taking. PR doesn't have problems means other ports is fine. So no problem in data acquisition system.
(3)Output connection. We check the difference between using 50 Om and not using. This connection noise comes from the resistance thermal noise, we also call it Johnson noise. Johnson noise is proportional to the resistance. But, there is no obvious difference. Or just 0.6 in motion of microrad. (It's hard to read because the motion of microrad keeps changing.)
So we think the problem comes from the Laser.
6.We check the saturation level of each actuator
By changing the offset, we check the output. Beyond a certain value, the output will keep increasing. This is the saturation level because the actuator cannot offer enough force. Details are shown in the attached photos.
So we need to read the sum value first and type it into our Labview program. This will make sure the right normalization.
7.Taking transfer function
We should note that the transfer function is measured in mechanical part(actuator part). So we insert the noise in port NOISE2, which is white noise. And then we should make sure the loop is closed. And we have a good PSD angle. Finally, we can start measuring.
Besides, there is another influencing factor. It is the driving matrix. We should take care.
8.Checking the PSD angle to reduce the coherence.
By changing PSD angle, we find a good angle to have the least coherence. The result is plotted and attached. But Yuefan said the optimal PSD angle will change overtime.
Measured the power of the probes with and without the surface calibration sample to check the transmission of the sample at different wavelengths
633nm: 2.87 mW -> 1.89 mW Transmission= 65%
1310nm: 24.8 mW -> 16.6 mW Transmission= 67%
----------------------------------------------------------------------------------------
To check linearity of the Si PD, I measured the HeNe power and changed it putting some filters while measuring the PD DC signal
2.87 mW -> 6.58V
2.44 mW -> 6.52V
1.45 mW -> DC=4.28V
1.22mW (2 filters) -> 3.4V
328uW -> DC=0.88V
Result: the PD is saturated, see plot
Manuel, Kuroki
We measured the beam waist of the probe at the detector.
We used a blade and a vertical micrometric stage to move the blade with steps of 0.5mm.
We did this for the 1310nm laser using a power meter for infrared lasers (and repeated the measurement twice).
Kuroki-san made the fit of the data with a gaussian cumulative function erf(x/c) where x is the blade position and c = w/sqrt(2)
Result: w = 2.57±0.05 mm
For the HeNe laser the power is too low, so the resolution of the power meter was not good, so we used the smaller one. The small one was too small for the size of the beam, so after the blade we put a lens (f=19mm) to focus the beam on the power meter.
Result: w = 2.40±0.05 mm
During the last week of September, the Infrared Mode Cleaner has been assembled in clean room using the same screw size used for the Green Mode Cleaner ( a bit different than the design due to availabililty and to avoid breaking).
To differenciate the 2 modes cleaner, one can look to the BMC connector : the blue one corresponds to the infrared and the yellow one to the green.
We might still need to make a holder for the BMC as we did for the green mode cleaner to avoid stress on the wires.
We were able to test this mode cleaner on the infrared path on the table and found a finesse of the order of 280 below the expected value given by the mirrors reflectivity (we expect between 312 and 520).
This might come from power and temporal fluctuations. We could see these fluctuations while testing the green mode cleaner but we were suspecting that they came from the power fluctuations coming from the SHG cavity.
These 2 fluctuations are reduced if we have more sampling points.
They are also reduced if the ramp frequency sent to scan the piezo actuator is reduced ( we could see a better stability by reducing the frequency from 20Hz to 5Hz).
We could also see some temporal shift between the ramp and the mode cleaner transmission.
It seems that this is due to some low pass filtering of the piezo driver because this shift can be seen between the output of the piezo driver and its monitoring output.
From the attached picture, it is visible that there is an excess of noise in the error signals. They look similar to the ones I observed when spikes started to appear.
The spike issue is reportend in entry 428 where I also give some reference values for the rms of the mirror motion in standard condition (where no spikes are present). The rms shown in the picture attached by Yuefan is about 7 microrad which is higher that the normal one (about 1 microrad). I'm not sure if the spikes are the only cause for the smaller range of the PR, anyway they make the local control very unstable and preventing the lock of the cavity.
It is good that PR magnet is back to life but I'm very surprised that it seemed not respondig for a period. Indeed something strange is going on...
Pic 2 (about BS), referred to in the text, is missing.
For the local control,while I was trying to change the matrix things, I tried again to test each magnet. It seems that the third magnet of PR which we thought it was lost, response to the noise very well. Then I test the magnet of the input, there is really one of the magnet lost. I am not sure what causes the no response of the PR magnet, the things I have changed is just the red beam position on all the aluminum mirror.
Yesterday I adjusted the PR local control again, so then I need also change the PSD angle, now the value is -0.045.
Also I rethought about the order we did everything, the reference was put after we realign the cavity by moving the picomotor. And after that we installed the AOM and the lenses, according to the reference we put on the bench and outside the PR chamber, now we already has the same alignment as before.But the range we can move the PR mirror is not large enough to put back the beam on the reference outside the BS chamber, which means also the PR range got smaller. The control of the PR and BS mirror was written in the same VI, so now I am a little bit suspect the program, but I am not able to check it in Labview.
There are something I cannot understand, should discuss with Eleonora later. The PR error signal has been put near 0 in both direction, when put offset of yaw at 0.9, the correction is -2.77, and if put offset at 1, the correction will suddenly saturate. For the BS, also for yaw if the offset is larger than 2, the correction signal looks like pulse.(pic 2)
From the attached picture, it is visible that there is an excess of noise in the error signals. They look similar to the ones I observed when spikes started to appear.
The spike issue is reportend in entry 428 where I also give some reference values for the rms of the mirror motion in standard condition (where no spikes are present). The rms shown in the picture attached by Yuefan is about 7 microrad which is higher that the normal one (about 1 microrad). I'm not sure if the spikes are the only cause for the smaller range of the PR, anyway they make the local control very unstable and preventing the lock of the cavity.
It is good that PR magnet is back to life but I'm very surprised that it seemed not respondig for a period. Indeed something strange is going on...
Pic 2 (about BS), referred to in the text, is missing.
We tried adjusting the distances of the parts in the IU to make the sharp image on the detector of a blade at 18mm after the crossing point.
We can make it a bit sharp. It is blurred because of diffraction.
We found the problem which the probe laser saturates the detector signal at 4V.
So, we put a neutral density filter (optical density = 2) in front of the laser and put a optical damp in order to remove the reflected beam by the filter. We measured a photodetector signal DC=2V, about half of the range (with laser current of 130mA)
We measured optical power ,which is 0.48 mW. (Before putting the filter, the power was 37.5 mW.)
After that, We measured a absorption signal of a reference sample.
We get it, but it have a low signal to noise ratio (AC=40mV). Also the phase shape of the scan is not as expected.
We think that imaging unit(IU) should be correctly aligned
Next step is that we should consider how to better align IU.
Maybe we can try a different position of the blade after the crossing point, and see if we get a better signal.
